The use of pedicle bone screws with an enlarged head supported in an opening of a receiver type device such as a plate, an implant or a tower or tulip type device is well known. The enlarged heads are typically supported in a complimentary seat at the base of the opening. During a surgical procedure, the screw is often held on assembly into a device. The pedicle or bone screw has threads adapted to engage bone. The bone can be pre-drilled or often the threads are of a self-tapping variety that drill themselves into the bone. Once fully threaded into the bone by a screw driver device, the screw ideally should not loosen. To insure this loosening does not occur, a variety of screw locking devices have been developed to prevent the screw from backing out of the bone and loosening. These added locking features are separate parts installed over the screw head typically, some are spring loaded devices that can deflect out of the path of the screw head on installation and snap over the screw head on tightening. The preferred locks are held in the device being anchored by the screw and automatically move into locking position so the surgeon does not need to do any additional steps to lock the screw in place.
These separate locking features add cost and complexity to the device being anchored. The need to avoid loosening bone screws, however, has justified this added burden.